Many systems, such as those in gas turbines, are subjected to thermally, mechanically and chemically hostile environments. For example, in the compressor portion of a gas turbine, atmospheric air is compressed to 10-25 times atmospheric pressure, and adiabatically heated to a temperature of from about 800° F. to about 1250° F. in the process. This heated and compressed air is directed into a combustor, where it is mixed with fuel. The fuel is ignited, and the combustion process heats the gases to very high temperatures, in excess of about 3000° F. These hot gases pass through the turbine, where airfoils fixed to rotating turbine disks extract energy to drive the fan and compressor of the turbine, and the exhaust system, where the gases provide sufficient energy to rotate a generator rotor to produce electricity. Tight seals and precisely directed flow of the hot gases provide operational efficiency. To achieve such tight seals in turbine seals and providing precisely directed flow can be difficult to manufacture and expensive.
To improve the efficiency of operation of turbines, combustion temperatures have been raised and are continuing to be raised. To withstand these increased temperatures, thermal barrier coatings (TBC) are often used as sealing structures for hot gas path components. An ability of the TBC to protect the hot gas path components from the rising temperatures is limited by a thermal conductivity of the TBC. The lower the thermal conductivity of the TBC, the higher the temperature the TBC can withstand.
An increased porosity in the TBC may decrease the thermal conductivity of the TBC. However, current methods of TBC deposition, including electron beam physical vapor deposition (EBPVD) and air plasma spraying (APS), are unable to form the desired porosity while maintaining a required mechanical strength in the TBC. Additionally, current TBC chemistries that have low K value constituents, like lanthana for example, cannot be deposited by APS to the thicknesses required for effective TBC layer due to the formation of a glass phase that disrupts the spraying process.
A fabrication process and an article that do not suffer from one or more of the above drawbacks would be desirable in the art.